Weird, eh? I’m happy to rely on a (mostly) battery-powered car. But I don’t want a battery-powered lawn mower. Even though I used a plug-in electric mower for years.
I swore off battery-driven power tools years ago. So, for me, it’s not as if this is some new stance.
In this post, I explain why. Why I’m not going for a battery-powered mower. And why I no longer buy any power tools that run on batteries.
Let me emphasize that my decision isn’t due to ignorance. If anything, it’s because I’ve had too much experience with big lithium-ion batteries.
A few things about lithium-ion batteries.
Practically speaking, your sole option for a walk-behind battery-powered mower is lithium-ion batteries. There have been some riding lawn mowers powered by lead-acid batteries. But I don’t think there’s anything on the market today not powered by lithium-ion batteries.
Point 1: Maybe you can recycle them.
Almost no lithium-ion batteries are recycled in the U.S.
I’m acutely aware of this because a) I bought a 200-pound lithium-ion add-on battery pack for my wife’s Prius in 2008, and b) recycling of those big lithium-ion batteries has been just around the corner for the past 15 years. I think my most recent post on that was Post #1715.
Still don’t believe that lithium-ion is rarely recycled? Here’s a handful of relatively recent references.
- About 1% of lithium-ion batteries are recycled.
- About 5% of lithium-ion batteries are recycled world-wide.
- Less than 5% are recycled in the U.S. and Europe.
That last reference is particularly illuminating. Read down to the part where the Federal government is still at the point of offering cash prizes for anybody who can figure out how to do it cost-effectively. Its not merely that lithium-ion batteries aren’t recycled, it’s really that there’s not even one good, standardized, agreed-upon process for doing it, let alone doing it cost-effectively.
Post #1712 has the details, but the reason for the lack of recycling is obvious. It costs money. Reportedly, Tesla currently pays $4/pound to recycle is lithium-ion batteries. Even with that, the cost of post-recycled lithium is higher than that of virgin lithium, making it an uneconomic source for production of new batteries.
Still, some stores — around here, notably Home Depot — have boxes where you can drop off old batteries weighing under 11 pounds. That should cover most lawn tool batteries.
That’s free to you because Home Depot covers the cost of processing those via call2recycle. This is an organization whose funding comes from battery- and battery-powered device manufacturers, or from organizations willing to pay to recycle those batteries. For example, their board of directors has representatives from Panasonic, Sony, Energizer, and Duracell, among others, based on their 2021 annual report.
You can see examples of their retail pricing on this page. It looks like they charge about $2.50 a pound to take boxes of mixed rechargeable batteries off your hands. So Home Depot is paying on-order-of $12 to allow you to dispose of a 5-pound lithium-ion lawn mower battery.
What happens after that is a bit unclear to me. For sure, the value of the materials recovered appears trivial. Here’s their 2021 Annual Report, showing revenue sources. Less than five percent of their revenues comes from the materials recovered from those batteries.
Source: call2recycle 2021 annual report.
They do not break out their collection and recycling costs separately. Combined, those account for the bulk of their costs.
At any rate, they are clearly at least paying to have those batteries disposed of properly. What fraction of the materials actually ends up in new products — is actually recycled — is not possible to determine from their annual report.
Interestingly enough, when I look up their lithium-battery recycling partners, the only U.S. partner appears to be a 2021 startup. Which again seems to emphasize just how iffy lithium battery recycling remains, at this time.
Fifteen years. For fifteen years, I’ve been living with a 200 pound LiFePO battery pack. And for fifteen years, large-scale lithium-ion battery recycling has been just around the corner. Which is right where it is today.
Point 2: Batteries trade lower fuel cost for higher capital consumption cost.
Which is a fancy way of saying, if you want to keep using the tool, you have to keep buying batteries.
We replaced the nickel-metal-hydride traction battery in my wife’s (now son’s) 2005 Prius somewhere around 178,000 miles. Doing the math, the cost of that new battery ate up roughly half of the total lifetime savings in gasoline costs, from driving that efficient hybrid compared to a similarly-sized non-hybrid 2005 vehicle.
But it’s not just the dollar cost. It takes quite a bit of energy to manufacture batteries, something that contributes to the multi-year “payback period” of a Prius relative to a non-hybrid automobile. For the first couple of years that you drive a hybrid, from a carbon-footprint standpoint, all you are doing with your lower fuel use is paying back the higher energy cost of the vehicle’s manufacturing.
In particular, worst-case (made-in-China, meaning, made using coal-fired electricity), large-format lithium ion batteries result in the release of roughly 200 kilograms of C02 per KWH of battery (calculated from this MIT reference, 16 metric tons per 80 KWH battery pack).
And so, creating a typical lawn-mower battery — 0.3 KW (72 volt, 4 amp-hour) would result in (200 KG/KW x 0.3 KW * 2.2 lbs/KG = ) 132 pounds of C02 released into the atmosphere.
I use 2 gallons of gas a year to mow my lawn. That generates about 40 pounds C02 per year. The upshot is that even if my electricity were carbon-free, I’d spend the first three years of battery-powered lawn mowing merely paying back that initial 132-pounds-of-C02 debt, for the manufacture of that disposable battery.
That’s not a huge surprise, to those of us who have been using big battery-powered objects. It was an estimated two year payback period for a 2005-era Prius, where the battery and motors didn’t really power the entire car. So, a three-year payback period for a small tool that’s entirely battery-powered? To me, based on my experience with the Prius, that seems entirely plausible.
As for the energy cost of the rest of it, I’ll just point to the high energy cost of smelting copper. Electric motors require quite a bit of that, which is another reason hybrids require more manufacturing energy than non-hybrid cars. Plausibly, depending on expected lifespan, there may be no manufacturing energy savings in the non-disposable portions of the devices.
For an extremely-long-lived battery, such as one used in a car, that payback period usually isn’t much of a consideration. You’re saving a ton of fuel, and the battery will typically last well over a decade. Overall, it’s a winner, even if you fully acknowledge the energy cost of producing the battery.
Here’s the kicker: How long do those lawn-mower batteries last? Every website I visit seems to give the same answer of three-to-five years. So they might last long enough to pay back that initial carbon-footprint debt.
The upshot is that a lithium-ion powered lawn mower is a fine way to reduce local air pollution. It may not be such a winner from the standpoint of reducing your carbon footprint. And since global warming/carbon footprint is my main concern, I’m not hugely attracted to those devices from an environmental standpoint.
In addition, knowing what I now know about lithium-ion batteries, I’d bet on the lower end of that three-to-five-year range. My wife’s new Prius — a Prius Prime — arguably contains a $12,000 lithium battery pack. With no warranty to speak of. So I got kind of serious about not trashing that. And that’s when I learned the rules for lithium-ion batteries. See Post #1703.
The rules, in brief: Lithium-ion batteries don’t like heat. They don’t like to be fast-charged. They don’t like rapid rates of discharge, either. And they really don’t like being worked from fully charged to fully dead. They much prefer shallow charge-discharge cycles.
And yet, every manufacturer seems intent on using them in all the wrong ways, in mowers. These will see highest use in the heat of summer, and typically be stored in a non-climate-controlled space. Everybody seems to charge their lawn-mower batteries at a “1 C” rate of charge or higher — from dead to fully charged in one hour. (Presumably, that’s to all ow you to swap batteries continuously and mow very large lawns.) I’m pretty sure manufacturers allow the full capacity of the battery to be used, unlike cars that reserve the top and bottom 10 to 15 percent as a buffer against over– and under-charging. (That’s why a 72-volt battery pack can be advertised as 80 volts, because once you’ve absolutely fully charged it, that’s what it’ll read, despite the fact that charging it to that degree is bad for battery life.)
Point 3: If you love buying name-brand inkjet cartridges, you’ll enjoy purchasing batteries for your lawn mower.
Here, I’ll just refer to the highest-rated 21″ walk-behind battery powered mower on Amazon. This is the Greenworks Pro 80V 21″ model, with 4.0 Ah battery.
On Amazon, the complete mower, with battery and charger, is $425. But the replacement 4.0 Ah battery, by itself, costs almost $300.
In short, your cost of the replacement battery is 70% of the total cost of the functioning lawn mower. And, as with power tools of all sort, manufacturers go way out of their way to make sure that only their batteries will fit their tools.
This, more than anything else, is why I swore off battery-powered shop tools. It’s the monopoly-exploitation aspect of the battery replacement. Once you’ve bought into a particular manufacturer’s line, they’ve got you. And as far as I was ever able to tell, generic batteries manufactured to fit those tools are all completely dreadful. So if you want a battery that works, for that name-brand tool, you pay that name-brand price.
Once I bought my third $45 battery pack, for my $60 drill, I did eventually figure out that a battery-powered drill is an expensive way to make holes in stuff. That drill eventually got to the point where battery packs were no longer available. (Which, if you own one long enough, will happen.) At that point, it too became just another particle in our great national solid waste stream. And was replaced by a corded drill.
Point 4: Caginess about power.
This is more of an irritation than a point of substance. But take any battery-powered lawn mower on the market, and try to find out the peak power of the electric motor, expressed either as kilowatts or as horsepower. Nobody will tell you that basic information.
At some level, the average power output is just basic physics. The mower above has a 72-volt, 4 amp-hour battery, and claims to be able to run for an hour on that. That should be sufficient to cut my half-acre lawn.
But do the math. How much energy is at your disposal, for that hour of mowing? Well, 72 volts x 4 amps = ~300 watts of average instantaneous output. Or, over the course of an hour, you have 0.3 KWH of power available to you, to accomplish your hour of mowing. For sure, your peak power output will be much higher than that. But if that battery is going to last an hour, it can’t put out more than an average of 300 watts, over that hour.
One horsepower is about 750 watts. So the average available power output is less than half a horsepower, if you’re going to get your hour of mowing out of that battery. Again, peak output will clearly be many multiples of that. But that’s what you have, to get through your lawn, on average, over the course of an hour.
In my case, there are parts of the lawn, at times of the year, that nearly stall the Honda 3.3 KW gas engine that runs my mower. I would love to know that some prospective battery-powered mower has a peak power output that meets or exceeds that 3.3 KW instantaneous power output.
But here, I bring up the last thing I know about lithium-ion batteries. If that battery could, in fact, produce 3.3 KW of instantaneous power, it would be discharging at more than a “10 C” rate. (That is, at that rate, the battery would be dead in less than one-tenth of an hour.) Discharges at rates like that are unambiguously bad for battery life, for traditional cylindrical-design lithium-ion cells. So even if it could match the peak power of my current mower, I’m not sure I’d want it to.
In other words, just as was true for my old corded Black-and-Decker, I’m pretty sure that the mower will get through my lawn. But I’m also pretty sure that I’m going to have to “baby” it when the going gets really tough.
But short of buying one and using it, there’s no way for me to tell, because manufacturers do not disclose peak power output of these mowers. And so, how well will some battery-powered mower cut through stands of uber-thick Zoysia grass?
Instead of providing me with the concrete information that would allow me to judge that, manufactures require that I take a guess. And when I see something like that, I assume it’s because their product would appear in an unfavorable light, if that information were disclosed.
Let me put it this way: If those battery-powered lawn mowers had peak power that exceeded that of a typical gas mower, you can bet that manufacturers would crow about it. So I think the absolute silence regarding peak power output tells me more-or-less all I need to know.
Point 5: Summary
For the time being, I’ve decided to continue using a gas-powered lawn mower. It’s a modern overhead-valve design, and (best guess, see prior post) mowing produces as much smog-forming pollution per hour as driving a mid-2010s-era sedan for an hour. That’s clearly a downside, compared to battery-powered mowing, but not an extreme one. For good measure, I’ve tossing my antiquated gas can in an effort to keep my gas-powered mowing as clean as possible.
My main environmental concern is global warming, and it’s not clear that a battery-powered mower offers much advantage there, compared to gas. That’s due to the carbon-intensive nature of lithium-ion battery production and the relatively short expected lifetime of those batteries in fairly harsh use conditions.
Otherwise, not switching to battery-powered mowing is mostly a question of avoiding annoyances. No mower maker will bother to tell me peak power. So I suspect that will be lacking. Each mower maker uses proprietary batteries. So I expect to pay an outrageous amount for them.
And the whole lithium-ion battery-recycling thing is one big question mark. Yes, you can drop your dead lawn mower batteries off at Home Depot, and Home Depot will cover the cost of getting them recycled, to some degree. The degree to which the material in these batteries is actually re-used is far from clear.
So that’s it. I saw a compelling reason and significant gains from switching car transportation to electricity. There, at issue was a considerable amount of gasoline burned per year, batteries with an extremely long projected life-span, and some guarantee of responsible end-of-life recycling via Toyota. Maybe. And the driving experience is better under electricity than with gas. For mowing the lawn, by contrast, at issue is just two gallons of gas a year, there’s no clear benefit in terms of carbon footprint, and I’m betting that it’s harder to mow with a battery-powered mower than with a modern gas mower.
So this is one area where I’m not going to electrify the task.
